1. Field of the Invention
This invention relates to an alloy suitable applicable to a magnetoresistive element, and a method of manufacturing the same.
2. Description of the Prior Art
Generally, a magneto-electric transducer is widely used as a contact-less switch, a switching element for a brushless electric motor or the like. Examples of the magneto-electric transducer are a semi-conductor Hall element, a semi-conductor magnetoresistive element, a planar Hall element and a ferromagnetic magnetoresistive element.
However, in the semiconductor element, the number of the carriers and the mobility are greatly influenced by temperature, and so the temperature characteristics are bad. Accordingly, the semiconductor element requires an external circuit for temperature compensation. The output voltage of the planar Hall element is low. Accordingly, for example, when it is used for driving the brushless electric motor, it requires a special peripheral circuit such as a high gain amplifier. Further, the unbalance voltage of the magnetoresistive element is high in comparison with the output voltage thereof, since the magnetoresistive element is a two-terminal element. Particularly, the change of the unbalance voltage due to the change of the resistivity with temperature cannot be neglected in comparison with the output voltage. Accordingly, the zero-point drift due to change of temperature comes into question for practical use.
The same assignee already filed the Japanese Patent Application (No. 79655/1973) corresponding to the U.S. Pat. No. 3,928,836 for a magneto-electric transducing element to overcome the above-described defects of the conventional magneto-electric transducing elements. The magneto-electric element includes two strips made of ferromagnetic material having magnetoresistive effect which are electrically connected to each other in series. The current paths of the two strips are perpendicular to each other. An output terminal is connected to the junction between the strips. Current supply terminals are connected to the opposite ends of the strips. In the corresponding U.S. Pat. No. 3,928,836, the above magneto-electric transducing element is stated as "a magnetoresistive element comprising an insulating substrate, a first current conducing ferromagnetic metal film strip on said substrate and having a current carrying ability predominantly in one direction, a second current carrying ferromagnetic metal film strip on said substrate having a current carrying ability predominantly in a direction substantially perpendicular to said one direction, first ends of said strips being connected together, a current input terminal connected to the opposite ends of said strips and an output terminal connected to the junction between the two strips."
When a magnetic field intensive enough to saturate the ferromagnetic strips is applied to the current path of the one strip at an angle .theta., the output voltage changes in proportion to (.DELTA..rho./.rho.o) cos 2.theta., where .DELTA..rho.=.rho..sub..parallel. -.rho..sub..perp., 2.rho..sub.o =.rho..sub..parallel.+.rho..sub..perp., .rho..sub..perp. represents the resistance when the saturable magnetization and the current are perpendicular to each other, and .rho..sub..parallel. represents the resistance when they are in parallel with each other. The change of the output voltage is maximum and minimum at the angle .theta.=0.degree. and 90.degree., respectively, where the switching operation is effected. The above described defects of the conventional magneto-electric transducing elements have been removed by the above magneto-resistive element.
However, some problems to be further solved have been found out on the above described magneto-resistive element.
Generally, in the manufacture of the magneto-resistive element, an Si (silicon) substrate is used from the view points of mass-production and cost-down. Since the Si substrate is thin, its strain resistivity is low. Accordingly, the saturation characteristic of the output of the magnetoresistive element is deteriorated. The characteristics of the magneto-resistive elements are much dispersed. The deterioration of the strain resistivity results in the central point potential deviation (the potential deflection of the junction between the two ferromagnetic strips) due to piezo-resistance effect. Accordingly, an expensive alumina substrate should be used for a contactless switch requiring high accuracy. Moreover, for the magnetoresistive element, it is preferable to select an alloy system whose magnetoresistive anisotropy ratio (.DELTA..rho./.rho.o) is large. The conventional alloy for such purpose is 76 Ni-24 Co alloy. However, its magnetostriction constant is large, and its strain resistivity is not improved.